The subject matter disclosed herein relates generally to an inlet air conditioning system for a gas turbine and, particularly, to an inlet air conditioning system and method with improved cooling of the inlet air.
A gas turbine typically includes: an inlet system, a compressor section, a combustion section, a turbine section, and an exhaust section. A gas turbine may operate as follows. The inlet system receives air from the ambient environment of the gas turbine, and the compressor section compresses inlet air. The compressed airstream then flows to the combustion section where fuel mixing may occur, prior to combustion. The combustion process generates a gaseous mixture that drives the turbine section, which converts the energy of the gaseous mixture to mechanical energy in the form of torque. The torque is customarily used to drive an electrical generator, a mechanical drive, or the like.
Gas turbine performance is commonly determined by output, thermal efficiency, and/or heat rate. The temperature and humidity of the incoming airstream have a significant impact on the gas turbine performance. Generally, the gas turbine becomes less efficient as the temperature of the airstream increases.
Various systems have been utilized to reduce the inlet airstream temperature, particularly during ambient conditions that have higher airstream temperatures and/or humidity. These systems attempt to achieve this goal by conditioning the airstream prior to entering the compressor section. Conditioning may be considered the process of adjusting at least one physical property of the airstream. The physical property may include, but is not limited to: wet-bulb temperature, dry-bulb temperature, humidity, and density. By adjusting one or more physical properties of the airstream, performance of the gas turbine can be improved.
Some known examples of these systems include: media type evaporative coolers, fogger evaporative coolers, chiller coils with mechanical water chillers, absorption water chillers with or without thermal energy systems, and the like. There are a few concerns, however, with known systems for conditioning the airstream entering a gas turbine.
In related inlet air cooling systems for turbine engines, both sensitive cooling and evaporative cooling systems are used. Sensitive cooling systems typically employ water chillers and cooling coils disposed within the inlet air stream. These systems are highly functional but are often considered too expensive to implement, at least in part due to the high expense of the cooling coils and water chiller plant, which may cost in the millions of dollars to fabricate and install. Evaporative cooling systems are typically considerably less expensive to fabricate and install, but work most optimally in hot and dry environments because hot, dry air provides greater cooling capabilities than a relatively humid environment. Indeed, evaporative coolers may have been completely discounted for use in high humidity environments due to their relatively poor performance compared to their use in hot and dry environments. Related evaporative cooling systems relied upon readily available water, such as water from a nearby water supply where the temperature of the water supply is tied to ambient conditions.
U.S. Pat. No. 8,365,530 (the '530 patent) discloses a system that includes both sensitive cooling and evaporative cooling. The '530 patent discloses a system where water is sprayed onto a media surface, and the water may be cooled or the water may be supplied at ambient conditions. This approach differs, in part, from evaporative cooling in that the media is different and the way in which the water is delivered—conventional evaporative cooling does not employ spraying.
Prior to the work that led to the present disclosure, it was accepted within the art that there was no benefit, at least with respect to efficiency, to chilling water for use with an evaporative cooler. Therefore the results discussed below, where improved efficiency of an evaporative cooler was achieved by supplying chilled water to an evaporative cooling media, were surprising and a substantial breakthrough. Indeed, devices according to the present disclosure provide effective cooling even with relatively high ambient humidity contrary to the accepted wisdom with respect to related evaporative coolers.